1. Field of the Invention
The present invention is directed to a catheter having a lumen for delivering drugs into the epidural space of a patient and electrodes for the relief of pain. More particularly, the present invention is directed to such a catheter that can be implanted in the patient temporarily or permanently. The permanent implantation embodiment includes a self-contained electrical pulse generator and a drug pump with a reservoir.
2. Description of Related Art
Electrical stimulation of the spinal column through electrodes implanted in the epidural space has been found useful in controlling pain. The use of injected anesthetics or narcotics has been found useful in the temporary relief of pain. In some instances, the local anesthetic or the narcotic is administered into the epidural spaces along the spinal column. These and other techniques are used to control intra-operative pain, post-operative pain and chronic pain states, such as those that might result from certain cancers. Such techniques as currently practiced, however, leave many patients without satisfactory pain relief.
This failure is result of the characteristics of the modalities for pain control and of the nerves that carry pain impulses. The nerve fibers carrying pain impulses to the spinal cord are classified into three major groups according to their speeds of conduction. Type A nerve fibers carry pain impulses at the rate of about 30 to 120 meters per second. Type B nerve fibers carry pain impulses at the rate of about 5-15 meters per second. Type C nerves carry pain impulses most slowly of all, about 0.1 to 2 meters per second. These fibers all relay impulses through an area in the spinal cord called the substantia gelatinosa. From this site, the nerve fibers are projected to the brain. The three primary modalities for pain control and their primary disadvantages are as follows.
First, local anesthetics may be injected into the epidural space. Local anesthetics act by blocking the transmission of pain impulses in types A, B, and C nerve fibers. Local anesthetics typically, however, relieve pain only a relatively short time and if large amounts are injected into the epidural space to achieve longer term pain relief, the local anesthetic is absorbed into the blood stream and leads to anesthetic toxicity. Consequently, typical anesthetics must be administered every hour or two. This requirement is labor intensive, provides numerous opportunities for serious treatment errors, leaves the patient in pain much of the time as the effectiveness of a dose fades, and may require repeated penetration of the epidural space, which causes scarring. Second, narcotics, such as morphine sulfate, or methadone, may be injected into the epidural space. Narcotics act by modulating the impulse transmission at the substantia gelatinosa. Narcotics are, however, extremely dangerous and may well spread upwards into the brain and lead to the arrest of breathing, and to death. Narcotics typically bring pain relief within from about 12-25 minutes and provide continuous pain relief for about 6-18 hours, depending on the particular narcotic used and the type of pain being treated. Because narcotics may be extremely addictive, physicians generally prefer to use non-narcotic pain relievers whenever possible. In addition, patients treated with epidural narcotics develop a tolerance for these drugs in which no amount of narcotic administered into the epidural space will effectively control pain, leaving the physician no option for relieving the patient's pain. Withholding the narcotics causes the state of tolerance to disappear after some time, and narcotic therapy can then be effectively resumed. In the meantime, however, other treatments must be resorted to if any pain relief is to be provided.
Third, an optimal amount of electrical stimulation of the spinal cord indirectly through the epidural spaces is used to relieve pain, but acts almost exclusively on the pain impulse traffic along the type C nerve fibers in the spinal nerves, leading to only a 50%-60% reduction in perceived pain. This modality is used in the treatment of pain from chronic inflammation, chronic pain from cancer, old injuries, nerve injuries, and so forth and can be permanently implanted, complete with its own subcutaneous power supply, for example, Trojan et al. U.S. Pat. No. 4,5349,556. Although it is useful for many patients, in many other patients electrical epidural nerve stimulation does not provide full, or even satisfactory pain relief.
In addition, in the case of an injected pain-relieving agent, whether local anesthetics or narcotics, the drugs quickly relieve pain but their pain killing ability dissipates over time due to absorption of the pain reliever by the body, which metabolizes the agent. Thus, the pain-relieving agent must be administered periodically and frequently. Typically, either local anesthetics or narcotics are administered every 2-6 hours (although some narcotics may provide pain relief for up to about eighteen hours in some cases). Even more importantly, it results in wide undulations in the level of pain experienced by the patient. When the anesthetic or narcotic is first administered, nearly all the pain vanishes. With the passage of time, however, the pain returns before the next dose is given. If doses are spaced closely enough to prevent the recurrence of pain, overdosing the patient may occur.
During surgical operations, anesthesia must be administered through a different method than is used to control post-operative pain. In some cases, even in a hospital, overdoses of narcotics lead of the deaths of patients.
Thus, it is clear that the prior art of pain relief includes some significant disadvantages.
Therefore, a need exist for a device and a process or method that achieves effective full-time satisfactory relief from serious pain; that reduces the likelihood of an overdose of an anesthetic or narcotic; and that permits application of a uniform dosage across time; and that permits the physician to establish anesthesia for surgery as well as to control post-operative pain using the same device for both functions; and that allows the physician to treat a patient with narcotics until tolerance develops and to easily replace the narcotic treatment with other effective treatments until the tolerance disappears, and then to easily resume narcotic treatment, all requiring a single penetration of the epidural space; and to provide such a pain-relieving device that can be implanted either temporarily or permanently.